The present invention relates to a method and a device for controlling a supplementary vacuum pump of the electrical type which is provided for supplementing brake booster vacuum for the braking system of an automotive vehicle, and more particularly relates to such a method and such a device for controlling such a vacuum pump, in which the control is improved so as to ensure good vacuum supply in conditions of high speed vehicle operation, while at the same time minimizing wear on the vacuum pump.
The present invention has been described in Japanese patent application Ser. No. 60-201136 (1985), filed by an applicant the same as the entity assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the text of said Japanese Patent Application and the claim and the drawings thereof; a copy is appended to the present application.
In Japanese Patent Laying Open Publication Ser. No. 59-164252 (1984), which it is not intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, there is disclosed a vacuum operated type of brake booster for the master cylinder of the braking system of an automotive vehicle, which receives a basic or main supply of manifold vacuum from a vacuum take out port provided in the intake system of the internal combustion engine of the vehicle, via a one way check valve, and which also receives a supplemental supply of vacuum from an electrically operated vacuum pump, via a second one way check valve. Thus, the usual type of vacuum supply from the intake system of the vehicle engine is used as the fundamental vacuum supply for the brake booster, but the vacuum pump is also operated so as to provide supplemental vacuum for said brake booster and so as to keep the vacuum value which is being provided for said brake booster at a predetermine vacuum level which is sufficient and appropriate.
However, this type of process and device as mentioned in the above identified proposal are only applicable to a vehicle with an engine that is fitted with an automatic stop device, and not to a conventional type of vehicle. Also, the operation of the pump is not controlled in response to the vacuum value actually present in the brake booster, so that in some circumstances this brake booster vacuum value may undesirably drop to be unacceptably low (close to atmospheric pressure).
The problem is that the force amplification characteristics of such a vacuum operated brake booster depend upon the vacuum value supplied to it, and to maintain suitable force amplification characteristic it is required to maintain the vacuum supplied to the brake booster at a high level and to keep the actual value of said vacuum within fairly tight limits, i.e. between an upper limit and a lower limit which differ from one another only by a relatively small value. However, the vacuum value which is received by the brake booster from the vacuum take out port provided to the intake system of the engine is variable, depending upon the current engine operational conditions, and particularly only has a relatively high value during engine idling or sharp engine braking operational conditions. Therefore, there arises a need to switch the electric vacuum pump on and off frequently, which has a deleterious effect upon the durability and the reliability of the pump.